Digital cameras have become one of the most popular of electronic devices. In a recent year, more digital cameras were sold than traditional film cameras. Images from digital cameras can be downloaded and stored on personal computers. Digital pictures can be converted to common formats such as JPEG and sent as e-mail attachments or posted to virtual photo albums on the Internet. Video as well as still images can be captured, depending on the kind of digital camera.
Digital cameras typically capture images electronically and ultimately store the images as bits (ones and zeros) on a solid-state memory. Flash memory is the most common storage for digital cameras. Flash memory contains one or more electrically-erasable read-only-memory (EEPROM) integrated circuit chips that allow reading, writing, and block erasing.
Early digital cameras required the user to download or transfer the images from the flash memory within the digital camera to a personal computer (PC). A standard serial cable was most widely used. However, the limited transfer rate of the serial cable and the large size of the digital images made such serial downloads a patience-building experience. Serial downloads could easily take half an hour for only a few dozen images.
Digital camera manufacturers solved this problem by placing the flash memory chips on a small removable card. The flash-memory card could then be removed from the digital camera, much as film is removed from a standard camera. The flash-memory card could then be inserted into an appropriate slot in a PC, and the image files directly copied to the PC.
FIG. 1A shows a flash memory card and adapter for transferring images from a digital camera to a PC. A user takes pictures with digital camera 14 that are stored in image files on flash memory chip(s). The flash memory chip is contained in CompactFlash card 16, which can be removed from digital camera 14 by pressing a card-eject button. Thus CompactFlash card 16 contains the image files.
While some smaller hand-held computers or personal-digital-assistants (PDA) have slots that receive CompactFlash cards, most PC's do not. Laptop or notebook PC's have PC-card (earlier known as PCMCIA, Personal Computer Memory Card International Association) slots that can receive PCMCIA cards. Many functions have been placed on PCMCIA cards, such as modems, Ethernet, flash memory, encryption keys, and even miniature hard drives.
CF-to-PCMCIA adapter 10 is a passive adapter that contains an opening that receives CompactFlash card 16. FIG. 1B shows CF-to-PCMCIA adapter 10 with CompactFlash card 16 inserted. Such CF-to-PCMCIA adapters 10 sell for as little as $5-10. CompactFlash is a trademark of SanDisk Corp. of Sunnyvale, Calif.
FIG. 1C shows a PC connected to a PCMCIA reader. Most laptop and notebook PC's contain one or two PCMCIA slots 22 that CF-to-PCMCIA adapter 10 can fit into. Then the user merely has to copy the image files from CompactFlash card 16 to the hard disk of PC 20. Since high-speed parallel buses are used, transfer is rapid, about the same speed as accessing the hard disk. Thus a half-hour serial-cable transfer can be reduced to less than a minute with the $5 CF-to-PCMCIA adapter.
Desktop PC's usually do not have PCMCIA slots. Then PCMCIA reader 12 can be used. PCMCIA reader 12 accepts CF-to-PCMCIA adapter 10 and connects to PC 20 through a parallel or high-speed Universal Serial Bus (USB) cable.
Multiple Flash-Card Formats
Although the CompactFlash card format is relatively small, being not much more than an inch square, other smaller cards have recently emerged. FIG. 2A illustrates various formats of flash-memory cards used with digital cameras. Many digital cameras still use CompactFlash card 16, which can be inserted into CF-to-PCMCIA adapter 10 for transfer to a PC. Other smaller, thinner formats have emerged and are used with some manufacturer's digital cameras. For example, SmartMedia card 24 is less than half an inch long, yet has enough flash memory capacity for dozens of images. SmartMedia-to-PCMCIA adapter 10′ is available commercially for about $60. The higher cost is believed to be due to a converter chip within adapter 10′. Also, different adapters 10′ are required for different memory capacities of SmartMedia card 24. SmartMedia is a trademark of the SSFDC Forum of Tokyo, Japan.
Other kinds of flash-memory cards that are being championed by different manufacturers include MultiMediaCard (MMC) 28 and the related Secure Digital Card (SD) 26. MMC is a trademark of SanDisk Corp. of Sunnyvale, Calif. while SD is controlled by the SD Group that includes Matsushita Electric Industrial Co., SanDisk Corporation, Toshiba Corp. Another emerging form factor from SONY is Memory Stick 18. Memory Stick has a PCMCIA/Floppy adapter while MMC has a floppy adapter.
The different physical shapes and pin arrangements of cards 24, 26, 28 and Memory Stick 18 prevent their use in CF-to-PCMCIA adapter 10. Indeed, most of these cards 24, 26, 28 have less than a dozen pins, while CompactFlash card 16 has a larger 50-pin interface. Furthermore, serial data interfaces are used in the smaller cards 24, 26, 28 while a parallel data bus is used with CompactFlash card 16.
FIG. 2B shows a Memory Stick-to-PCMCIA adapter using an active converter chip. Memory Stick 18 fits into an opening in Memory Stick-to-PCMCIA adapter 15, allowing adapter 15 and the Memory Stick to be plugged into a standard PCMCIA slot on a PC. However, adapter 15 has an integrated circuit (IC) converter chip 11 within it. Converter chip 11 may be needed to convert the serial data format of Memory Stick 18 to the parallel data format of a 68-pin PCMCIA slot. Inclusion of converter chip 11 in adapter 15 significantly increases the cost and complexity of adapter 15 compared to CF-to-PCMCIA adapter 10 which is a passive adapter without a converter chip.
While the advances in flash-memory card technology are useful, the many different cards formats present a confusing array of interface requirements to a PC. Different adapters are needed for each of the card formats. PCMCIA card reader 12 can be replaced with other format readers, such as a SmartMedia Card reader, and even some multi-standard readers are available, such as a universal reader from Lexar Media that reads CompactFlash or SmartMedia in addition to PCMCIA.
What is desired is a universal adapter for flash-memory cards of several different formats. An adapter that accepts SmartMedia, MultiMediaCard, Secure Digital, and Memory Stick cards is desired. A flash-card reader with a single slot that accepts any format card using the adapter is desired. Special detection logic on the flash reader is desired to distinguish between the many flash-card formats is desirable. A low-cost passive adapter is desired that does not need an expensive converter chip. A multi-format reader is desired for a PC. A stand-alone flash reader is desired that can copy image files from flash cards without a PC is also desired.